Hi—
I just got back in July from working as an au pair in Spain, and I had no problems leaving after overstaying. I got there in a year ago in September, and since I was going to come back to the US for Christmas, I was worried they wouldn’t let me back in after that. I booked my return ticket for day 88 so that I would have two days left legally and, just to be safe, I booked a cheap flight to London for day 90, in case I was asked to prove I was leaving the Schengen zone. All of that turned out to be unnecessary (although maybe still a good precaution to take—your boyfriend could buy a cheap flight to England for within the 90 days in case he’s asked to show something). When I went back after Christmas, I flew into Paris, and they didn’t pay any attention to the fact that I had only two days left legally. After that I didn’t leave the EU until late July, and, again, they didn’t pay any attention.
The one thing I would recommend is not flying Ryanair if he’s going to travel around the EU while he’s overstaying. Ryanair has you check in online and then go through some “document check desk” where supposedly they make sure that you have the proper documentation to enter your destination country. I don’t know if they even catch people often this way, but it seems like one of the only times you’re likely to run into trouble, since Ryanair has a reputation for causing as many problems as possible. I had booked a Ryanair flight from Rome back to Spain when I was traveling at the end, but I got scared about what would happen at the document check desk once I found out about it, so I ended up getting another ticket with EasyJet, and that was fine.
So obviously there are no guarantees, and I don’t know anything about new laws that might crack down on overstaying Americans, but my experience went perfectly smoothly. Good luck!
—Maria